1. Field of the Invention
This invention relates to a fluid flow meter for indicating the rate of flow through a fluid transport line and in particular the rate of flow of a liquid fuel being consumed by an internal combustion engine.
2. Description of the Prior Art
One common method of measuring the fuel consumption of an internal combustion engine is to cause the fuel to flow through a vertically oriented tapered tube having a movable member therein. As the fuel flow rate increases the differential pressure forces the movable member into a higher position within the tube where a correspondingly larger space is available for fuel to flow around the movable member. While this method is quite satisfactory for research and development projects on internal combustion engines, it is rather impractical for consumer operated motor vehicles. Various electronic methods of sensing the position of the movable member of this type have been proposed but are generally either too expensive, too inaccurate, or both.
Another well known method for measuring fuel flow rate is to pass the fuel over the blades of a turbine or through a vane-type metering device similar to a vane pump. In actual construction, these devices have a relatively limited range of flow rates for which useful accuracy can be expected. Inaccuracies generally arise due to the wide pressure variations present under ordinary operating conditions or the bearing friction inherent in most turbine designs. Furthermore, the analog read-out devices most easily adapted and normally used with fuel flow metering devices of this type are either inherently expensive, relatively inaccurate or both. These devices are typically difficult to use due to the short term fuel flow variations inherent in the stop-and-go urban traffic patterns. It is difficult if not completely impossible to translate these short term variations into a long term fuel flow average value.
Another method commonly used for test track evaluation of fuel flow is to install a three way valve between the fuel pump inlet and the gas tank with a third port connected to a graduated cylinder of known volume, such as one-tenth of a gallon. The driver manually operates these valves and visually observes the rate of fuel consumption from the graduated container. The valve must then be returned to the fuel tank position and the graduated cylinder refilled or the engine will stop running due to a lack of fuel. The convenience of this fuel flow measuring device leaves much to be desired since the graduated container must be filled by manual techniques. Even though this type of fuel flow measuring device is extremely accurate over a very wide range of flow rates, it is obviously impractical and in some cases unsafe for use on a vehicle operating under normal highway conditions.
It is therefore the object of this invention to produce a simple and inexpensive device, capable of accurately indicating the fuel consumption of an engine over a very wide range of engine sizes and operating conditions without the requirement of extensive fuel system modifications. It is a further object of this invention that no manual operations be required of the operator at any time subsequent to the initiation of the metering interval, which, if neglected, could cause the engine to stop running for a lack of fuel.
It is a further object of this invention to eliminate analog read-out devices since they are relatively expensive, inaccurate and difficult to interpret under normal operating conditions. Another object of this invention is that the fuel flow measurement apparatus must operate with a pressure drop which is small enough under all conditions so as to be negligible when compared to the pressure available from normal automotive fuel pumps.